In general, a waste heat recovery system for reusing heat of water wasted from a place where a great deal of hot water is used, such as a public bath, a swimming pool, a fish-farm, or other place, heats cold water inside a heat exchange pipe in such a manner that the heat exchange pipe for carrying cold water is installed inside a water tank and waste water of high temperature discharged from the public bath is induced into the water tank so as to transfer heat between the heat exchange pipe and the waste water. However, in the conventional waste heat recovery system, the waste water is strained through a filter before being induced into the water tank to prevent stopping of the water tank or a flow channel due to foreign matters because foreign matters or wastes contained in the waste water are induced into the water tank. However, the conventional waste heat recovery system has a problem in that it is difficult to transfer heat smoothly as the foreign matters are stained on the external surface of the heat exchange pipe or sludge is formed on the external surface of the heat exchange pipe in spite of installation of the filtering device while the waste heat recovery system is used for a long time. Therefore, the water tank has a cover or a hole for cleaning, and so, a user can remove the foreign matters using a brush. However, it is difficult to clean a conduit and the heat exchange pipe since the conduit and the heat exchange pipe are in a spiral form or have a complicated shape to increase the surface area for heat transfer.